The invention relates to the field of recording and playback of real-time information.
The invention relates to a method of recording real-time information and control information related thereto in a recording area on a record carrier arranged according to a recording format, in which method the real-time information is subdivided into cells and in which playback parameters for reproducing sequences of the cells are included in the control information.
The invention further relates to a device for recording real-time information and control information related thereto in a recording area on a record carrier arranged according to a recording format, the device comprising recording means arranged for subdividing the real-time information into cells and for including playback parameters in the control information for reproducing sequences of the cells.
A method of recording real-time information on a record carrier is known from EP 814475. Real-time information is information having a real-time nature to be reproduced at a prescribed rate, usually audio or video information, or a combination of audio and video. In the known method video information is encoded digitally and subdivided into cells, which are short, but independently reproducible segments of the real-time information, while corresponding audio information may be included in the cells. Control information for accessing and reproducing the real-time material is generated for enabling several playback functions. A user playable program usually called a title, for example a movie, is constituted by a sequence of cells and corresponding control information, in which the sequence is defined by playback parameters. The control information is generated separately after the video material has been gathered and stored temporarily in a memory, e.g. on a video tape. The user may play the movie at standard speed, or he may scan the material in trick play modes, e.g. fast forward or slow motion. The control information may further comprise different sequences built out of the same video material, or further pointers for accessing any moment within the real-time material for jumping to specific scenes. The way the control information and the real-time information are provided on a record carrier is standardized to enable players of different brands to reproduce the material. An example of such a standard is the DVD-video standard, of which the relevant aspects, such as control information, are described in said EP 814475. The real-time information and control information are finally transferred to the record carrier by well known mastering and reproducing steps, e.g. pressing optical discs from a metal master disc. A problem of the known recording method is, that a temporary storage of the real-time information is required before the control information can be generated. On the final product, the record carrier, the control information is to be positioned according to the format rules, which prescribe that the control information precedes the real-time information. However the control information is generated after all real-time material is known and stored temporarily. Hence the known method of recording is complicated and expensive, in particular in view of home recording.
The above citations are hereby incorporated in whole by reference.
It is an object of the invention to provide a recording method and device in which real-time information can be recorded according to an existing format and which is less complex.
For this purpose, the method as described in the opening paragraph is characterized in that the method comprises the steps of first selecting a starting point within the recording area different from the beginning of the recording area for creating a free area between the beginning of the recording area and the starting point, thereafter recording the real-time information from the starting point, and recording the control information in said free area. The device as described in the opening paragraph is characterized in that the recording means are arranged for first selecting a starting point within the recording area different from the beginning of the recording area for creating a free area between the beginning of the recording area and the starting point, thereafter recording the real-time information from the starting point, and recording the control information in said free area. Creating the free area has the effect, that a real-time recording can be made in one pass, i.e. the real-time information is recorded on a record carrier of a writable type directly at its final location without temporary storage, while the control information is generated during recording. The control information may be stored temporarily in a memory, e.g. in a buffer IC. It is to be noted, that the amount of digital data for the control information is substantially smaller than the amount of data for the real-time information, usually less than 1%. Hence a memory for temporary storage is inexpensive, and the recording device is suitable for home recording.
The invention is also based on the following recognition. Formats intended for mastered and mass produced record carriers of a read-only type usually prescribe a non-causal order in which the control information precedes the recorded audio/video, because this is the order playback devices require the information for reproduction. Non-causality inherently arises during recording, because one cannot calculate sequences and pointers for video material not yet available, in particular if the video is compressed to a variable length digital code such as MPEG2. For a professional recording studio this presents no problem, as the audio/video material is always stored temporarily, e.g. on a master video tape, before the final authoring process, in which the control data is calculated, is performed. In a home recorder one-pass recording is required, and therefore the DVD-video format seems unsuitable. However the inventors have seen, that the prescribed non causal ordering can be achieved by reserving space at the beginning of the record carrier and generating a basic set of control information and playback parameters during the recording of the real-time information itself. The generated control information is stored in a temporary memory, and written to the reserved area as soon as possible, e.g. directly when a stop recording command is received or even during real-time recording when buffering is available for the real-time recording process. Although a few parameters may have to be calculated or re-calculated after completing the real-time recording, this requires only a short time, and remains substantially unnoticed by the user. Hence the user perceives a recording in one pass, while the record carrier still is compatible to the existing format and can be played on standard players, e.g. a DVD-video player.
Preferred embodiment of the device the recording means are arranged for recording elements of the control information on the record carrier during recording the real-time information. This embodiment has the advantage that less temporary memory is needed. In practice a substantial part of the control information consists of elements relating to the cells, e.g. a table of pointers to each cell. A first part of such a table can be saved from the temporary memory to the record carrier while the recording of further cells still continues, because this first part is not affected by the further cells.